The invention relates to a reception method using a TDMA multiple-access method, the reception method receiving connection establishing signals placed in time slots, and receiving the transmitted signals that vary in strength from the time slots and amplifying the received signals with an amplification coefficient of a particular size.
In a radio system subscriber terminals, like mobile phones, are located at different distances from the base station. Path attenuation weakens a transmitted signal, in which case the power of the signals, transmitted with the same transmission power, vary as the signals arrive at the receiver. Various interference signals generated as a result of signal reflection can be summed as reversed in phase to an information signal, which then attenuates even more. The further apart the receiver and the transmitter are located from each other the more the various obstacles can attenuate the signal. If the signal attenuates enough, the connection between the subscriber terminal and the base station may be disconnected or the connection may not be established at all.
In radio systems connections are established using signals of different frequencies. The signals can also be transmitted by appropriately interleaving them into time slots. In prior art solutions frequency allocation during a call is performed in such a manner that the subscriber terminals located far from the base station are allocated to use a particular frequency. A signal propagated far over the radio path has typically needed a lot of strengthening in the receiver. Subscriber terminals located close to the base station are allocated to use some other frequency which has deviated from the signal frequency used by the subscriber terminal located far from the base station. If the signal distance from the transmitter to the receiver has been short, then the signal has typically been strengthened only slightly in the receiver.
Digital tuners are commonly used in the base station receivers of the radio systems. Typically a receiver comprises multiple tuners enabling the dynamic range of the receiver to be divided into smaller parts. Each tuner forms a specific part of the entire dynamic range of the receiver. In practice, the receivers have covered different frequency ranges, and the receivers have then together been able to receive signal on a predetermined frequency band. The dynamic range of the base station has thus been extensively increased.
In addition, the base stations use wideband multi-carrier radios allowing the size of the base stations to become smaller and lighter and the price to become more advantageous. The multi-carrier radios enable the different base station functions to be improved, and the operation of the base station thus becomes more flexible. If the powers of the signals the base station receives are variable, then automatic gain control (AGC) cannot be used in the receiver, since in practice the gain cannot be reduced only on the basis of a strong signal. As a result of the above, a weak signal cannot be received at all in said situation. Similarly on the basis of the weak signal, the gain cannot in practice be raised, since a strong signal would then gain too much and become distorted.
The lack of automatic gain control requires the receiver to have a very wide dynamic range. For example, in the GSM system the dynamic range of the base station receiver should be about 100 dB. Such a dynamic range cannot be implemented using current technology. Particularly the components performing the A/D conversion of the receiver restrict the increase of the dynamic range.
It is an object of the present invention to provide a reception method and a receiver so as to solve the above problems. This is achieved with the type of reception method presented in the preamble, characterized by forming at least two sets of time slots composed of time slots using amplification coefficients of varying sizes, and amplifying signals received from the time slots of the same set of time slots with an amplification coefficient of the same size, and placing a connection establishing signal into the set of time slots so as to measure the strength of the received signal and to place the connection establishing signal into the set of time slots on the basis of the signal strength measurement performed for the received signal.
The invention also relates to a receiver used in a TDMA radio system receiving signals placed in time slots enabling the receiver to establish connections, the receiver receiving the signals, which are placed in the time slots and vary in strength, and comprising amplification means for amplifying the received signals with an amplification coefficient of a particular size.
The receiver is characterized by being arranged to receive connection establishing signals from time slots and to form at least two sets of time slots from the time slots, and the amplification means of the receiver amplifying the signals included in various sets of time slots with an amplification coefficient of a different size, and the amplification means amplifying the signals included in the same set of time slots with an amplification coefficient of the same size, and the receiver comprising measurement means for measuring the strength of the signal received by the receiver, and placing means for placing the connection establishing signal into a set of time slots based on the strength measurement performed for the received signal.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on determining the time slot used on the connection between the transmitter and the receiver on the basis of the measurement performed for the signal received by the receiver.
The reception method and the receiver of the invention provide several advantages. The method enables the receivers to receive signals from frequency ranges that are identical, different or partly overlapping. Thus, the number of channels can be increased. In this method the time slots are grouped into sets of time slots. The time slot signals that belong to the same set of time slots are amplified in the amplification means with the same amplification coefficient. The number of amplification means can thus be minimized.